A Theoretical Discussion of a Menisci Micropump Driven by an Electric Field

2006 ◽  
Vol 129 (4) ◽  
pp. 404-411 ◽  
Author(s):  
Alexandru Herescu ◽  
Jeffrey S. Allen
Keyword(s):  
Electric Field ◽  
Fluid Motion ◽  
Liquid Interfaces ◽  
Vapor Bubbles ◽  
Liquid Phases ◽  
The Stability ◽  
Novel Concept ◽  
Enhanced Boiling ◽  
Stability Limits ◽  
Induced Dipoles

The potential for miniaturization of analytical devices made possible by advances in micro-fabrication technology is driving demand for reliable micropumps. A wide variety of micropumps exist with many types of actuating mechanisms. One such mechanism is electrohydrodynamic (EHD) forces which rely upon Coulomb forces on free charges and/or polarization forces on induced dipoles within the liquid to induce fluid motion. EHD has been used to pump liquid phases and to displace gas–liquid interfaces for enhanced boiling heat transfer as well as to displace gas/vapor bubbles. A novel concept for using EHD polarization forces to deflect a stationary meniscus in order to compress and pump a gaseous phase is described. The pumping mechanism consists in alternative compression of two gas volumes by continuous deflection of the two pinned menisci of an entrapped liquid slug in an electric field. Using the Maxwell stress relations, the electric field strength necessary to operate the pump is determined. The operational limits are determined by analyzing the stability limits of the two menisci from inertial and viscous standpoints, corroborated with the natural frequencies of the gas–liquid interfaces.

Stability as a constraint in sagittal plane human force exertion modeling

1998 ◽  
Vol 1 (1) ◽  
pp. 23-39
Author(s):  
Carter J. Kerk ◽  
Don B. Chaffin ◽  
W. Monroe Keyserling
Keyword(s):  
Muscle Strength ◽  
Ankle Joint ◽  
Coefficient Of Friction ◽  
Sagittal Plane ◽  
Biomechanical Model ◽  
Whole Body ◽  
The Stability ◽  
Joint Center ◽  
Static Conditions ◽  
Stability Limits

The stability constraints of a two-dimensional static human force exertion capability model (2DHFEC) were evaluated with subjects of varying anthropometry and strength capabilities performing manual exertions. The biomechanical model comprehensively estimated human force exertion capability under sagittally symmetric static conditions using constraints from three classes: stability, joint muscle strength, and coefficient of friction. Experimental results showed the concept of stability must be considered with joint muscle strength capability and coefficient of friction in predicting hand force exertion capability. Information was gained concerning foot modeling parameters as they affect whole-body stability. Findings indicated that stability limits should be placed approximately 37 % the ankle joint center to the posterior-most point of the foot and 130 % the distance from the ankle joint center to the maximal medial protuberance (the ball of the foot). 2DHFEC provided improvements over existing models, especially where horizontal push/pull forces create balance concerns.

Directionality and the Role of Polarization in Electric Field Effects on Radical Stability

2017 ◽  
Vol 70 (4) ◽  
pp. 367 ◽  
Author(s):  
Ganna Gryn'ova ◽  
Michelle L. Coote
Keyword(s):  
Electric Field ◽  
External Electric Field ◽  
Radical Reactions ◽  
Electric Field Effects ◽  
Dissociation Energies ◽  
Barrier Heights ◽  
Diol Dehydratase ◽  
Group A ◽  
Activity Of Enzymes ◽  
The Stability

Accurate quantum-chemical calculations are used to analyze the effects of charges on the kinetics and thermodynamics of radical reactions, with specific attention given to the origin and directionality of the effects. Conventionally, large effects of the charges are expected to occur in systems with pronounced charge-separated resonance contributors. The nature (stabilization or destabilization) and magnitude of these effects thus depend on the orientation of the interacting multipoles. However, we show that a significant component of the stabilizing effects of the external electric field is largely independent of the orientation of external electric field (e.g. a charged functional group, a point charge, or an electrode) and occurs even in the absence of any pre-existing charge separation. This effect arises from polarization of the electron density of the molecule induced by the electric field. This polarization effect is greater for highly delocalized species such as resonance-stabilized radicals and transition states of radical reactions. We show that this effect on the stability of such species is preserved in chemical reaction energies, leading to lower bond-dissociation energies and barrier heights. Finally, our simplified modelling of the diol dehydratase-catalyzed 1,2-hydroxyl shift indicates that such stabilizing polarization is likely to contribute to the catalytic activity of enzymes.

Self-Assembly of Monolayers of Submicron Sized Particles on Thin Liquid Films

2013 ◽  
Author(s):  
Shriram Pillapakkam ◽  
N. A. Musunuri ◽  
P. Singh
Keyword(s):  
Electric Field ◽  
Self Assembly ◽  
Uv Light ◽  
Capillary Forces ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Liquid Interfaces ◽  
Uv Curable ◽  
Particle Monolayer ◽  
Uv Curable Resin

In this paper, we present a technique for freezing monolayers of micron and sub-micron sized particles onto the surface of a flexible thin film after the self-assembly of a particle monolayer on fluid-liquid interfaces has been improved by the process we have developed where an electric field is applied in the direction normal to the interface. Particles smaller than about 10 microns do not self-assemble under the action of lateral capillary forces alone since capillary forces amongst them are small compared to Brownian forces. We have overcome this problem by applying an electric field in the direction normal to the interface which gives rise to dipoledipole and capillary forces which cause the particles to arrange in a triangular pattern. The technique involves assembling the monolayer on the interface between a UV-curable resin and another liquid by applying an electric field, and then curing the resin by applying UV light. The monolayer becomes embedded on the surface of the solidified resin film.

Numerical Simulations of Electric Field Driven Self-Assembly of Monolayers of Mixtures of Nanoparticles

2017 ◽  
Author(s):  
E. Amah ◽  
N. Musunuri ◽  
Ian S. Fischer ◽  
Pushpendra Singh
Keyword(s):  
Electric Field ◽  
Physical Properties ◽  
Numerical Simulations ◽  
Self Assembly ◽  
Composite Particle ◽  
Critical Value ◽  
Direct Numerical Simulations ◽  
Composite Particles ◽  
Liquid Interfaces ◽  
Induced Dipole

We numerically study the process of self-assembly of particle mixtures on fluid-liquid interfaces when an electric field is applied in the direction normal to the interface. The force law for the dependence of the electric field induced dipole-dipole and capillary forces on the distance between the particles and their physical properties obtained in an earlier study by performing direct numerical simulations is used for conducting simulations. The inter-particle forces cause mixtures of nanoparticles to self-assemble into molecular-like hierarchical arrangements consisting of composite particles which are organized in a pattern. However, there is a critical electric intensity value below which particles move under the influence of Brownian forces and do not self-assemble. Above the critical value, when the particles sizes differed by a factor of two or more, the composite particle has a larger particle at its core and several smaller particles forming a ring around it. Approximately same sized particles, when their concentrations are approximately equal, form binary particles or chains (analogous to polymeric molecules) in which positively and negatively polarized particles alternate, but when their concentrations differ the particles whose concentration is larger form rings around the particles with smaller concentration.

scholarly journals Electro-responsive polyelectrolyte-coated surfaces

2017 ◽  
Vol 199 ◽  
pp. 335-347 ◽  
Author(s):  
V. Sénéchal ◽  
H. Saadaoui ◽  
J. Rodriguez-Hernandez ◽  
C. Drummond
Keyword(s):  
Electric Field ◽  
Smart Materials ◽  
Electrical Stimulus ◽  
Colloidal Dispersions ◽  
Polymer Chains ◽  
Molecular Response ◽  
Coated Surfaces ◽  
The Stability ◽  
Induced Changes ◽  
Applied Fields

The anchoring of polymer chains at solid surfaces is an efficient way to modify interfacial properties like the stability and rheology of colloidal dispersions, lubrication and biocompatibility. Polyelectrolytes are good candidates for the building of smart materials, as the polyion chain conformation can often be tuned by manipulation of different physico-chemical variables. However, achieving efficient and reversible control of this process represents an important technological challenge. In this regard, the application of an external electrical stimulus on polyelectrolytes seems to be a convenient control strategy, for several reasons. First, it is relatively easy to apply an electric field to the material with adequate spatiotemporal control. In addition, in contrast to chemically induced changes, the molecular response to a changing electric field occurs relatively quickly. If the system is properly designed, this response can then be used to control the magnitude of surface properties. In this work we discuss the effect of an external electric field on the adhesion and lubrication properties of several polyelectrolyte-coated surfaces. The influence of the applied field is investigated at different pH and salt conditions, as the polyelectrolyte conformation is sensitive to these variables. We show that it is possible to fine tune friction and adhesion using relatively low applied fields.

scholarly journals Variation principle in calculating the flow of a two-phase mixture in the pipes of the cooling systems in high-rise buildings

2018 ◽  
Vol 33 ◽  
pp. 02063 ◽  
Author(s):  
Andrey Aksenov ◽  
Anna Malysheva
Keyword(s):  
Channel Cross Section ◽  
Variation Principle ◽  
Two Phase ◽  
Liquid Phases ◽  
Rate Of Increase ◽  
Annular Layer ◽  
Gas Liquid Flow ◽  
The Stability ◽  
Air Conditioning Systems ◽  
Physical Laws

The analytical solution of one of the urgent problems of modern hydromechanics and heat engineering about the distribution of gas and liquid phases along the channel cross-section, the thickness of the annular layer and their connection with the mass content of the gas phase in the gas-liquid flow is given in the paper.The analytical method is based on the fundamental laws of theoretical mechanics and thermophysics on the minimum of energy dissipation and the minimum rate of increase in the system entropy, which determine the stability of stationary states and processes. Obtained dependencies disclose the physical laws of the motion of two-phase media and can be used in hydraulic calculations during the design and operation of refrigeration and air conditioning systems.

Macro-scale description of transient electro-kinetic phenomena over polarizable dielectric solids

2009 ◽  
Vol 620 ◽  
pp. 241-262 ◽  
Author(s):  
G. YOSSIFON ◽  
I. FRANKEL ◽  
T. MILOH
Keyword(s):  
Electric Field ◽  
Electrolyte Solution ◽  
Time Scale ◽  
Temporal Evolution ◽  
Fluid Motion ◽  
Double Layers ◽  
Uniform Field ◽  
Micro Particles ◽  
Macro Scale ◽  
Dielectric Solids

We have studied the temporal evolution of electro-kinetic flows in the vicinity of polarizable dielectric solids following the application of a ‘weak’ transient electric field. To obtain a macro-scale description in the limit of narrow electric double layers (EDLs), we have derived a pair of effective transient boundary conditions directly connecting the electric potentials across the EDL. Within the framework of the above assumptions, these conditions apply to a general transient electro-kinetic problem involving dielectric solids of arbitrary geometry and relative permittivity. Furthermore, the newly derived scheme is applicable to general transient and spatially non-uniform external fields. We examine the details of the physical mechanisms involved in the relaxation of the induced-charging process of the EDL adjacent to polarizable dielectric solids. It is thus established that the time scale characterizing the electrostatic relaxation increases with the dielectric constant of the solid from the Debye time (for the diffusion across the EDL) through the ‘intermediate’ scale (proportional to the product of the respective Debye- and geometric-length scales). Thus, the present rigorous analysis substantiates earlier results largely obtained by heuristic use of equivalent RC-circuit models. Furthermore, for typical values of ionic diffusivity and kinematic viscosity of the electrolyte solution, the latter time scale is comparable to the time scale of viscous relaxation in problems concerning microfluidic applications or micro-particle dynamics. The analysis is illustrated for spherical micro-particles. Explicit results are thus presented for the temporal evolution of electro-osmosis around a dielectric sphere immersed in unbounded electrolyte solution under the action of a suddenly applied uniform field, combining both induced charge and ‘equilibrium’ (fixed charge) contributions to the zeta potential. It is demonstrated that, owing to the time delay of the induced-EDL charging, the ‘equilibrium’ contribution to fluid motion (which is linear in the electric field) initially dominates the (quadratic) ‘induced’ contribution.

The tuning effect of the electric field on the physical properties of some typical wurtzite semiconductors

2017 ◽  
Vol 31 (33) ◽  
pp. 1750310 ◽  
Author(s):  
Jia-Ning Li ◽  
San-Lue Hu ◽  
Hao-Yu Dong ◽  
Xiao-Ying Xu ◽  
Jia-Fu Wang ◽  
...  
Keyword(s):  
Electric Field ◽  
Physical Properties ◽  
First Principles ◽  
Electronic Structures ◽  
Density Functional ◽  
Great Influence ◽  
Semiconductor Materials ◽  
Functional Theory ◽  
The Stability ◽  
Wurtzite Semiconductors

Under the tuning of an external electric field, the variation of the geometric structures and the band gaps of the wurtzite semiconductors ZnS, ZnO, BeO, AlN, SiC and GaN have been investigated by the first-principles method based on density functional theory. The stability, density of states, band structures and the charge distribution have been analyzed under the electric field along (001) and (00[Formula: see text]) directions. Furthermore, the corresponding results have been compared without the electric field. According to our calculation, we find that the magnitude and the direction of the electric field have a great influence on the electronic structures of the wurtzite materials we mentioned above, which induce a phase transition from semiconductor to metal under a certain electric field. Therefore, we can regulate their physical properties of this type of semiconductor materials by tuning the magnitude and the direction of the electric field.

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